ATHENS, Greece (AP) _ It was 1975, two days before Christmas. Three men approached Richard Welch, the CIA's station chief in Athens, as he returned home from a party. One pulled out a .45-caliber pistol and shot the bespectacled 46-year-old American dead.

The slaying signaled the birth of the shadowy November 17 terrorist organization, now the most feared group in Greece and one of the deadliest in Europe.

Since that fateful night, its signature .45 has been used to kill six more of its 20 victims, which include three other American officials and one employee, two Turkish diplomats and 13 Greeks. The rest have been killed by another .45, bombs and anti-tank missiles. The group has also staged 35 other attacks on tax offices and multinational companies.

None of its members has been arrested in those two decades, and their identities remain a mystery to Greek, American and European police and intelligence agencies.

``From then until now, Greece is the only country where it has been impossible to not only smoke out terrorism but even to make a single substantial strike against it,'' said Lefteris Papadimitriou, a conservative politician and one of a handful of people to survive a November 17 attack.

It is a striking failure.

Italy's Red Brigades were effectively wiped out by 1987. The Red Army Faction in Germany was decimated, with more than 30 of its top members serving long prison sentences. Action Direct in France also was wrecked.

And other European extremist groups, including Basque, Corsican and Irish separatists, have had many of their members arrested.

No one has ever linked November 17 to other radical organizations, although the Greek group's bomb-making methods indicate some of its members may have been trained in the Middle East during the early 1970s.

One of the few people to believe in a connection is Stelios Papathemelis, a former Socialist public order minister who tried to get information from the files of the former East German secret police.

``When the first proof started coming, that was when I was forced to resign. From that point on others have to explain,'' he wrote in an article published Dec. 21 without elaboration.

Papathemelis, who left his post in 1994, has refused to expand on his comment, saying only in an interview: ``I still think we need international cooperation so we can gather enough information to do the job effectively.''

His replacement, Sifis Valyrakis, will not comment on the issue of terrorism.

Police and security officials are unsure of November 17's origins although all agree its members number from 10 to 25 people.

Many think its founders were part of a resistance group formed by Socialist Premier Andreas Papandreou during the 1967-75 military dictatorship and went their own way after democracy was restored.

According to published reports, the ailing Papandreou has hinted that he has suspicions about their identities, but it is speculation he probably will take to the grave.

The group is named for the day in 1973 when the military junta sent tanks and soldiers to crush a student uprising at the Athens Polytechnic University.

Marxist-Leninist in ideology, November 17 is anti-American, anti-NATO, anti-European Union and in recent years extremely nationalist. It has called for an armed uprising against the middle and upper classes.

There are strong indications that November 17 may have connections to other Greek extremists groups that may also have fermented during the junta's years. They include the leftist Popular Revolutionary Struggle, which has carried out dozens of nonlethal bomb attacks since 1974.

But police also have failed to arrest any member of that group, which many security officials believe to be a training ground for the deadlier November 17.

One security official, who spoke on condition of anonymity, said November 17 is unique because it does not appear to want to spearhead any political movement.

But its attacks over the years have swung along with local political perceptions. Many Greeks despised the junta and blamed the United States for supporting it, and in its first decade of operation, November 17 targeted Americans and police officers who served the dictatorship.

Turkey's occupation of Cyprus in 1974 made Turkish diplomats the group's prey. Greek businessmen and politicians, perceived to be representatives of the ruling class, also have become targets.

The end of the Cold War seems to have created an ideological problem for November 17 and its targets shifted. Its more recent attack was last May and was aimed at the private Mega television network, which November 17 described as a capitalist tool. Police say it was pure chance that no one was killed when two anti-tank rockets were fired into the building.

In an effort to turn up the heat, police announced in mid-December a plan to spend nearly $30 million to revamp the anti-terrorism services. The United States and Greece have also offered more than $2 million in reward money.

But security officials are uncertain money alone will ever stop November 17. ``We just hope they make a mistake one day,'' one said privately.